1 ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University L5 Optical Fiber Link and LAN Design.

1ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University

L5

Optical Fiber Link and LAN Design

L5

Optical Fiber Link and LAN Design


Table of contentTable of content

Transmission Type

Elements in Network Design

Factors for Evaluating Fiber Optic System Design

Link Budget Considerations

Power Budget

Power Budget Requirement

Example : Long-haul Transmission System

Example : LAN


Table of content (cont.)Table of content (cont.)

Bandwidth Budget

System Rise Time

Example on STM-4, STM-16 and STM-64

Budget Summary

Sensitivity Analysis

Eye Diagrams

Signal to Noise Ratio (SNR)

Cost/ Performance Considerations

Summary


Transmission TypesTransmission Types

Two types of transmissions:1. Link (point to point)

2. Networka. point to multipointb. Meshc. Ring


Elements of Link/ Network DesignElements of Link/ Network DesignTransmitter :

Operating wavelength (), Linewidth (),Rise time, Bit-rate, Line format, Power level

Fiber : SMF/MMF, Fiber type – SMF28, DSF, etc, Cable loss, Spool length

Rx : PSEN, PSAT, Rise time


Elements of Link/ Network Design (cont.) Elements of Link/ Network Design (cont.)

Connection:

No. of splice, Splice loss

No. of connectors, Connector Loss

In Line Devices:

Splitter, Filter, Attenuator, Amplifier Insertion loss, Gain


The Main Problems

Attenuation and Loss

Dispersion

The Main Question

In Digital System

- Data Rate

- Bit Error Rate

In Analog System

- Bandwidth

- Signal to Noise

Ratios


System Factor Considerations Type of Fiber Single-mode or Multimode Operating Wavelength 780, 850, 1310 and 1550 nm

typical Transmitter Power Typically expressed in dBm Source Type LED or Laser Receiver Sensitivity and Overload Characteristics

Typically expressed in dBm

Detector Type PIN Diode, APD or IDP

Factors for Evaluating Fiber Optic System Design


System Factor Considerations Modulation Code AM, FM, PCM or Digital Bit Error Rate (BER) (Digital Systems Only)

10-9 ,10-12 Typical

Signal to Noise Ratio Specified in decibels (dB) Number of Connectors Loss increases with the number of

connectors Number of Splices Loss is Loss increases with the

number of splices Environmental Requirements

Humidity, Temperature, Exposure to sunlight

Mechanical Requirements Flammability, Indoor/Outdoor Application

Factors for Evaluating Fiber Optic System Design (cont.)


Optical Transmitter/ Sources Optical Transmitter/ Sources

LEDs

Output Power

Modulation Bandwidth

Center Wavelength

Spectral Width

Source Size

Far-Field Pattern

Laser Diodes• Output Power• Modulation

Bandwidth• Center Wavelength,

Number of Modes• Chirp, Linewidth• Mode Field of the

Gaussian beam


Optical FiberOptical Fiber

Multimode Fiber

Attenuation

Multimode Dispersion

Chromatic Dispertion

Numerical Aperture

Core Diameter

Single-Mode Fiber• Attenuation• Chromatic

Dispersion• Cutoff Wavelength• Spot Size


Optical Receiver/ PhotodiodeOptical Receiver/ Photodiode

• Risetime/Bandwidth

• Response Wavelength Range

• Saturation Level

• Minimum Detection Level


Simple Link Simple Link

TX RX

Medium and Devices

OA

OA


Link Budget ConsiderationsLink Budget Considerations

Three types of budgets:

(1) Power Budget

(2) Bandwidth or Rise Time Budget

(3) ?


POWER BUDGETPOWER BUDGET


Power Budget Requirements: PB : PRX > PMIN

PRX = Received PowerPMIN = Minimum Power at a certain BER

PRX = PTX – Total Losses + Total Gain - PMARGIN

PTX = Transmitted Power

PMARGIN ≈ 6 dB


Requirements Cont’d:Requirements Cont’d:

Loss,L = LIL + Lfiber + Lconn. + Lnon-linear

LIL = Insertion Loss

Lfiber = Fiber Loss

Lconn.= Connector Loss

Lnon-linear= Non-linear Loss

Gain,G = Gainamp + Gnon-linear

Gainamp = Amplifier Gain

Gnon-linear = Non-linear Gain


dB, dBm, mWdB, dBm, mW

dB = 10 log (P1/P2)dBm Value % of 1 mW Power Application

0.0 100% 1.0 mW Typical laser Peak Output

-13.0 5% 50.0W Typical PIN Receiver Sensitivity

-30.0 0.1% 1.0W Typical APD Receiver Sensitivity

-40.0 0.01% 100.0W Typical LED Peak Output


dB Power Out as a % of Power In

% of Power Lost

Remarks

1 79% 21% - 2 63% 37% - 3 50% 50% ½ the power 4 40% 60% - 5 32% 68% 6 25% 75% ¼ the power

7 20% 80% 1/5 the power

8 16% 84% 1/6 the power

9 12% 88% 1/8 the power

10 10% 90% 1/10 the power

Decibel to Power Conversion


dB Power Out as a % of Power In

% of Power Lost

Remarks

25 0.3% 99.7% 1/300 the power

30 0.1% 99.9% 1/1000 the power

40 0.01% 99.99% 1/10,000 the power

50 0.001% 99.999% 1/100,000 the power

Decibel to Power Conversion


IS THIS SYSTEM GOOD?

Example: Power Budget Measurement for Long

Haul Transmission

PTx = 0 dBm

185 km

PSEN = -28 dBm

Splice

Attenuation Coefficient, = 0.25 dB/km

Dispersion Coefficient, D = 18 ps/nm-km

Number of Splice = 46

Splice Loss = 0.1 dB

PMargin = 6 dB

Connector Loss = 0.2 dB

Connector


CONCLUSION: BAD

SYSTEM!!

Simple Calculation….

Fiber Loss = 0.25 dB/km X 185 km = 46.3 dB

Splice Loss = 0.1 dB X 46 = 4.6 dB

PMargin = 6 dB

Total Losses = 46.3 + 4.6 + 0.4 = 51.3 dB

Power Budget, PRX < PSEN !!

PRX = -57.3 dB

PRX = PTX – Total Losses – PMargin

= 0 – 51.3 – 6

Connector Loss = 0.2 dB X 2 = 0.4 dB


How To Solve?Answer…Place an

amplifierBut… What is the gain value??

Where is the location?And…


First we calculate the amplifier’s gain..

Gain PSEN - PRX

Gain -28 – (-57.3)Gain 29.3 dB

To make it easy,Gain 30 dB

Now…Where to put the amplifier?


Three choices availablefor the location

Power Amplifier – At the transmitter

Preamplifier – At the receiver

In Line – Any point along fiber


Let us check one by one…

Power Amplifier: PTX + Gain = POUT 0 + 30 = 30

dBmBut is there any power amplifier with 30 dBm POUT? NO, THERE ISN’T

Hence …


What about Preamplifier?

POUT received = -57 dBm

Remember…

Preamplifier with 30 dB available?Yes

But, can it take –57 dBm?

Typically, NO

Hence …


Let us check In Line Amplifiers

30 dB gain amplifier available here…

But, What value can it take?

Typically –30 dBm

So…

Now, we can find the location…


Where is the –30 dBm point?

PTX – Loss At That Point = 0 dBm – 30 dB

Loss At That Point = -30 dBm

30 = x Length of That PointRemember = 0.25,Point Length = 30/0.25

= 120 kmBut 120 km from Tx,

No. of splice = 120/4

= 30

Assume Other Loss = 0, Loss At That Point = Fiber Loss,

Splice Loss = 0.1 dB x 30 = 3 dB


Also remember connector loss at amplifier and Tx…

2 connectors

Connector Loss = 0.2 dB x 3 = 0.6 dB

Total Losses = Fiber Loss + Splice Loss + Connector Loss

Actually, at 120 km,

= 30 + 3 + 0.6 = 33.6 dB

33.6 dB > 30 dB!! NOT GOOD!

Now, We have excess of 3.6 dB…Find the distance,

Fiber Loss Length = 3.6/0.25 = 14.4 km

Good Location = 120 km – 14.4 km = 105.6 km

+ 1 connector at Tx


Let us confirm the answer…At 105.6 km from Tx,

Fiber Loss = 0.25 x 105.6 = 26.4 dB

No. of Splice at 105.6 km = 105.6/4 =26.4 = 27

Splice Loss = 0.1 x 27 = 2.7 dB

Total Losses = 26.4 + 2.7 = 29.1 dB

29.1 dB < 30 dB !!CONFIRM…105.6 KM IS A GOOD LOCATION!!

PTx = 0 dBm

185 km

PSEN = -28 dBmSplice Connector

105.6 KM


IS THIS SYSTEM GOOD?

PTx = -15 dBm

500 m

Using

850nm PSEN = -25 dBmAttenuation Coefficient, = 4.5 dB/km

Dispersion Coefficient, D = 18 ps/nm-km

Number of Splice = 0

Splice Loss = 0 dB

PMargin = 2 dB

Connector Loss = 0.5 dB

Server A Server B

Example: Power Budget Measurement for LAN


BANDWIDTH BUDGET

BANDWIDTH BUDGET


Calculate the total rise times Tx, Fiber, Rx

Calculate Fiber rise time, TFiber

Tfiber = D x x L

D = Dispersion Coefficient = LinewidthL = Fiber Length

Tx Rise Time, TTX = normally given by manufacturerRx Rise Time, TRX = normally given by manufacturer

System Rise TimeSystem Rise Time


Total Rise time, Tsys:

Tsys=1.1(TTX2+TRX

2+Tfiber2)1/2


Bandwidth BudgetBandwidth Budget

TX RX

Medium and Devices

T’

Δτ = T’ - T

T

OA

OA


What is a good Rise time?

For a good reception of signalTsys < 0.7 x Pulse Width (PW)

PW = 1/BitRate for NRZ1/2BitRate for RZ


Example: Rise Time Budget Measurement

for Long Haul Application

Tx rise time, TTX = 0.1 nsRx rise time, TRX= 0.5 nsLinewidth() = 0.15 nm

Dispersion Coefficient, D = 18 ps/nm-kmFiber length = 150km

Bit Rate = 622MbpsFormat = RZ


Fiber rise time, TF =Length x D x Linewidth() = 150 km x 18 x 0.15 nm

= 0.4 ns

Total Rise time, TSYS = 1.1 TLS2 + TPD

2 + TF

2 = 1.1 0.01 + 0.25 + 0.16

Simple Calculation….

TSYS = 0.77 ns


Let say,Bit Rate = STM 4 = 622 MbpsFormat = RZ

Tsys < 0.7 x Pulse Width (PW)

Pulse Width (PW) = 1/(622x106)

= 1.6 ns

0.77 ns < 0.7 x 1.6 ns

0.77 ns < 1.1 ns !!

Good Rise Time Budget!!


Let say,Bit Rate = STM 16 = 2.5 GbpsFormat = RZ

Tsys < 0.7 x Pulse Width (PW)

Pulse Width (PW) = 1/(2.5x109)

= 0.4 ns

0.77 ns < 0.7 x 0.4 ns

0.77 ns ≥ 0.28 ns !!

Bad Rise Time Budget!!


Budget SummaryBudget Summary Option Power

BudgetBandwidth

BudgetFinancial

A Source (LED vs. LD)

Δλ

850nm Mediocre Bad Cheap

1310nm Good Good Less expensive

1550nm Very good Very good Expensive

Modulation Bandwidth

LED NA Bad Cheap

LD NA Good Expensive

Output Power LED Mediocre NA Cheap

LD Good NA Expensive

Radiation pattern LED (far-field pattern)

NA Bad Cheap

LD (Gaussian beam)

NA Good Expensive


Budget SummaryBudget Summary

B Fiber Option Power Budget

Bandwidth Budget

Financial

Attenuation MM Mediocre Mediocre Cheap

SM Good Good Expensive

Dispersion MM Mediocre Mediocre Cheap


Numerical Aperture (NA)

MM Mediocre Mediocre Cheap


Core Diameter MM Mediocre Mediocre Cheap



Budget SummaryBudget SummaryC Receiver (PIN vs.

APD)

Option Power Budget

Bandwidth Budget

Financial

Rise time/ Bandwidth

PIN Mediocre Mediocre Cheap

APD Good Good Expensive

Response wavelength range



Saturation Level PIN Mediocre Mediocre Cheap


Minimum detection level




Sensitivity AnalysisSensitivity Analysis

Minimum optical power that must be present at the receiver in order to achieve the performance level required for a given system.


Factors will affect this analysisFactors will affect this analysis

1. Source Intensity Noise - Refers to noise generated by the LED or Laser

Phase Noise - the difference in the phases of two optical wavetrains separated by time, cut out of the optical wave

Amplitude Noise - caused by the laser emission process.

2. Fiber Noise

Relates to modal partition noise

3. Receiver Noise

Photodiode, conversion resistor


4. Time Jitter and Intersymbol Interference

Time Jitter - short term variation or instability in the duration of a specified interval

Intersymbol Interference

result of other bits interfering with the bit of interest

inversely proportional to the bandwidth

Eye diagrams - to see the effects of time jitter and intersymbol interference


5. Bit error rate - main quality criterion for a digital transmission system

BER = Q [IMIN2/ (4 . N0 . B) ]

where :

N0 = Noise power spectral density (A2/Hz)

IMIN = Minimum effective signal amplitude (Amps)

B = Bandwidth

Q(x) = Cumulative distribution function (Gaussian distribution)


Eye Diagrams


Signal to Noise RatioSignal to Noise Ratio

SNR = S/NS - represents the information to be transmitted

N - integration of all noise factors over the full system bandwidth

SNR (dB) = 10 log10 (S/N)


Cost/Performance ConsiderationsCost/Performance Considerations

Components considerations such as : Light Emitter Type

Emitter Wavelength

Connector Type

Fiber Type

Detector Type


SummarySummary

The key factors that determine how far one can transmit over fiber are transmitter optical output power, operating wavelength, fiber attenuation, fiber bandwidth and receiver optical sensitivity.

The decibel (dB) is a convenient means of comparing two power levels.

The optical link loss budget analyzes a link to ensure that sufficient power is available to meet the demands of a given application.


SummarySummary

Rise and fall times determine the overall response time and the resulting bandwidth.A sensitivity analysis determines the amount of optical power that must be received for a system to perform properly.Bit errors may be caused by source intensity noise, fiber noise, receiver noise, time jitter and intersymbol interference.The five characteristics of a pulse are rise time, period, fall time, width and amplitude.


TUTORIALTUTORIAL


Thank YouThank You

1 ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University L5 Optical Fiber Link and LAN Design.

Documents

Transcript of 1 ETM7172 OPTICAL COMMUNICATION SYSTEMS Multimedia University L5 Optical Fiber Link and LAN Design.